This invention relates to a control apparatus for an internal combustion engine which can stop the supply of fuel to a misfiring cylinder of the engine.
In an internal combustion engine, due to breakage of parts, poor electrical connections, or malfunction of equipment such as the ignition coil, combustion occasionally does not take place properly in one or more cylinders of the engine and so-called "misfiring" occurs. Due to misfiring, a mixture of uncombusted fuel and air is discharged from the engine.
Many automobiles are equipped with a catalytic converter for removing harmful components from the engine exhaust gases. A typical catalytic converter is a three-way catalytic converter which simultaneously oxidizes carbon monoxide and hydrocarbons while it reduces oxides of nitrogen (NOx). In order for a catalytic converter to function effectively, it is important that the air-fuel ratio for the engine be near the stoichiometric ratio and for the fuel to be properly combusted in the cylinders.
When misfiring takes place in an engine, the uncombusted air-fuel mixture which is discharged from the engine flows into the catalytic converter, and a sudden chemical reaction takes place, causing an enormous increase in the temperature of the catalytic converter. Under these conditions, the catalytic converter can not function properly, and harmful exhaust gases are discharged into the atmosphere. The increase in temperature also produces degradation of the catalytic converter and shortens its life span. Furthermore, when an automobile is stationary, if dead grass or other combustible material should contact the catalytic converter when it is at an abnormally high temperature due to misfiring, there is the possibility of a fire starting.
It is therefore highly desirable to be able to detect a misfiring cylinder and stop the supply of fuel to that cylinder. One type of conventional misfiring sensor monitors the voltage across the primary winding of the ignition coil of an engine. This voltage normally has a prescribed periodic nature which is determined by the rotational speed of the engine. If the period of the voltage is irregular and a voltage is not generated at proper intervals, it is determined that the ignition coil or some other portion of the ignition system is malfunctioning and that misfiring is taking place. The misfiring sensor then generates a warning in the form of a warning light or buzzer and sends control signals to the engine control apparatus, which cuts off the supply of fuel to the cylinders.
However, the above-described conventional misfiring sensor is only able to detect misfiring due to malfunctions of the ignition system in or on the upstream side of the ignition coil. It is unable to detect misfiring due to problems with equipment on the downstream side of the ignition coil, such as spark plugs, the distributor, or connecting wires, and it is unable to detect misfiring due to problems with other systems of the engine, such as the fuel supply system of the engine. Thus, there are many cases in which a conventional misfiring sensor cannot detect misfiring.